The invention relates to a blind rivet nut having a head forming an annular flange and a shank comprising a head end, a foot end, and a cylindrical bore extending in lengthwise direction from the head end to the foot end, closed at the foot end of the shank and having a second bore segment neighboring the head end whose diameter is greater than the diameter of the first bore segment, the wall surrounding the second bore segment forming a plastically deformable portion of the shank and having an outer surface formed as a regular polygon, in particular a hexagonal prism.
Blind rivet nuts are employed chiefly in thin-walled parts, in particular made of sheet metal, to provide them with a fastening thread that can serve for fastening a stud or a bolt. Blind rivet nuts may also serve to connect two or more thin-walled parts to each other. Blind rivet nuts may, for example, be employed in the sheet-metal roofs of automobiles so that a roof member or roof railing may be attached thereto. For such applications, blind rivet nuts are made with closed end so that a tight closure of the roof is obtained after insertion of the blind rivet nut.
Blind rivet nuts of the kind specified are disclosed in EP 0589144 A1, EP 0634582 A1 and WO 02/081936 A1.
In fastening blind rivet nuts of the specified kind, the problem arises that the forces acting on the thin-walled or sheet-metal part accommodating the blind rivet nut may deform the sheet-metal or other thin-walled part in such manner that uniform contact with the flange of the blind rivet nut is no longer obtainable. This is especially disadvantageous if a tight connection, preventing passage of a liquid or gaseous medium, is to be made between the blind rivet nut and the sheet-metal or other thin-walled part. Another problem arises in the fastening of the blind rivet nut, in achieving a sufficiently great radial extent of the polygonal bulge formed in the deformation of the deformable region on the blind side.
The object of the invention is to create a blind rivet nut of the kind initially mentioned that is simply and reliably installable and affords a uniform contact, suitable for sealing, of the flange with the part accommodating the nut after termination of the process of deformation.